The use of vegetable protein, especially soy protein, is receiving greater attention due to its health benefit claims. There is an increased interest to develop technology to incorporate soy protein into juice type acid beverages. The concern, however, is the suspendibility of soy protein in acidic beverages at or near its isoelectric point where the solubility of soy protein is at a minimum. Soy protein will naturally precipitate over time due to gravitational forces based on Stokes' Law. The rate of the formed sediment is proportional to the diameter of the soy protein, coupled with the viscosity of the acid beverage. High viscosity and smaller particles will suppress the development of sediment. A process method, in addition to the use of a stabilizer, will greatly suppress the rate of sediment formation. The processing method employed is homogenization of the fully formulated acid beverage by the use of an ultra high pressure homogenization of up to 30,000 pounds per square inch
Stokes' Law is an equation relating the terminal settling velocity of a smooth, rigid sphere in a viscous fluid of known density and viscosity to the diameter of the sphere, when subjected to a known force. Stokes' Law will correctly predict that for two small steel balls, one having a radius exactly twice the other, the bigger ball will fall through a fluid of known viscosity four times faster than the smaller ball does through a fluid of the same viscosity. The bigger ball has eight times the weight and twice the drag force for the same velocity, and the drag force is proportional to the velocity.
Juices and other acidic juice-like beverages are popular commercial products. Consumer demand for nutritional healthy beverages has led to the development of nutritional juice or juice-like beverages containing protein. The protein provides nutrition in addition to the nutrients provided by the components of the beverage. Recently it has been discovered that certain proteins have specific health benefits beyond providing nutrition. For example, soy protein has been recognized by the United States Food and Drug Administration as being effective to lower blood cholesterol concentrations in conjunction with a healthy diet. In response, there has been a growing consumer demand for acidic juice-like beverages containing proteins that provide such specific health benefits.
A hurdle to adding protein to acidic beverages, however, is the relative insolubility of proteins in an aqueous acidic environment. Most commonly used proteins, such as soy proteins and casein, have an isoelectric point at an acidic pH. Thus, the proteins are least soluble in an aqueous liquid at or near the pH of acidic beverages. For example, soy protein has an isoelectric point at pH 4.5 and casein has an isoelectric point at a pH of 4.7, while most common juices have a pH in the range of 3.7 to 4.0. As a result, protein tends to settle out as a sediment in an acidic protein-containing beverage-an undesirable quality in a beverage.
Protein stabilizing agents that stabilize proteins as a suspension in an aqueous acidic environment are used to overcome some of the problems presented by protein insolubility. Pectin is a commonly used protein stabilizing agent.
Pectin, however, is an expensive food ingredient, and manufacturers of aqueous acidic beverages containing protein desire less expensive stabilizers, where the amount of required pectin is either reduced or removed in favor of less expensive stabilizing agents.
U.S. Pat. No. 5,232,726 (Clark et al., Aug. 3, 1993) relates to a method for extending the shelf life of juices, particularly citrus juice such as orange juice, without pasteurization, by subjecting the juice to an ultra high pressure homogenization step of 15,000 pounds per square inch or greater.
U.S. Pat. No. 5,286,511 (Klavons et al., Feb. 15, 1994) provides a beverage such as orange juice that is clouded by a suspension of soy protein particles, where the protein particles are prevented from aggregating to the point of settling out by pectin. Pectin inhibits the protein from settling by adsorbing to individual protein particles and imparting an overall negative charge to the protein particles, resulting in repulsion of the particles from one another, and thereby preventing the protein particles from aggregating and settling out of the suspension. Pectin also increases the viscosity of the beverage, which helps stabilize protein particles against gravitational forces.
U.S. Pat. No 6,696,084 (Pace et al., Feb. 24, 2004) relates to a spray drying process for the preparation of pharmaceutical compositions containing small particles of phospholipid-stabilized fenofibrate. Prior to spray drying, a heated suspension of molten fenofibrate is subjected to a two stage homogenization. The first pressure stage is from 2000 to 30,000 pounds per square inch.
U.S. Pat. No 6,221,419 (Gerrish, Apr. 24, 2001) relates to a pectin for stabilizing proteins particularly for use in stabilizing proteins present in aqueous acidified milk drinks. It must be understood that the inclusion of pectin has both desirable and undesirable effects on the properties of acidified milk drinks. While pectin can act as a stabilizer against sedimentation of casein particles or whey separation, it can have the disadvantage of increasing the viscosity of the drink due to its cross-linking with naturally co-present calcium cations rendering the drink unpalatable. It will be seen that in the absence of pectin, there is significant sedimentation in the case of both drinks caused by the instability of the casein particles which also results in relatively high viscosity. After a certain concentration of pectin has been added, the casein particles become stabilized against sedimentation after which increasing the pectin concentration has little effect on sedimentation. Turning to the viscosity of the drinks, this also significantly drops on stabilisation of the casein particles but then almost immediately begins to rise again due to cross-linking of the excess pectin added by the co-present calcium cations. This increased viscosity is undesirable as it leads to the beverage having poor organoleptic properties. This range may be as narrow as only 0.06% by weight of pectin based upon the beverage weight as a whole. Below this working range, sedimentation is a significant problem, whereas above it, the viscosity of the beverage is undesirably high.